Anion Gap
Calculate the serum anion gap from basic metabolic panel values. Used to differentiate causes of metabolic acidosis. Normal range: 8–12 mEq/L (without K⁺ correction).
Results
What is it?
Calculates the serum anion gap from basic metabolic panel values using the formula: AG = Na⁺ − (Cl⁻ + HCO₃⁻). The anion gap quantifies unmeasured anions in blood and is the primary tool for classifying metabolic acidosis. Normal range is 8–12 mEq/L (without potassium).
How to use
Enter sodium (Na⁺), chloride (Cl⁻), and bicarbonate (HCO₃⁻) values from your basic metabolic panel, all in mEq/L. The calculator subtracts the sum of measured anions from sodium to reveal the gap occupied by unmeasured anions.
Example scenario
Na⁺ = 140, Cl⁻ = 102, HCO₃⁻ = 24: AG = 140 − (102 + 24) = 14 mEq/L (slightly elevated). In diabetic ketoacidosis, you might see Na⁺ = 138, Cl⁻ = 98, HCO₃⁻ = 12: AG = 28 mEq/L — a markedly elevated gap indicating accumulation of ketoacids.
Pro tip
Remember MUDPILES for elevated anion gap causes: Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates. Always correct for albumin: for every 1 g/dL drop in albumin below 4, add 2.5 to the expected anion gap.